The present disclosure relates to voltage selection circuitry and a direct current-to-direct current (DC-to-DC) converter that includes the voltage selection circuitry. A DC-to-DC converter can increase or decrease an input voltage and output the increased or decreased input voltage to an output terminal. A DC-to-DC converter can be incorporated into various electronic devices, such as a portable electronic device and a display device. For example, a voltage needed to drive a passive matrix organic light emitting diode (OLED) display can be approximately 18 volts (V), but a source voltage of a lithium ion battery may be approximately 3.7 V. Thus, a boost type DC-to-DC converter may be needed to drive the passive OLED.
FIG. 1 is an example circuit diagram of a conventional DC-to-DC converter. The conventional DC-to-DC converter includes a switch unit 1 and a switch control circuit unit 2. The driving voltage for driving the switch control circuit unit 2 can be basically supplied from an output terminal of the switch unit 1.
For example, if the conventional DC-to-DC converter illustrated in FIG. 1 is a boost type DC-to-DC converter, a period in which an output voltage is lower than an input voltage inevitably occurs according to the characteristics of a rising curve of an output voltage of the DC-to-DC converter. However, if such a low output voltage is applied as a driving voltage for driving the switch control circuit unit 2, the operation of the switch control circuit unit 2 becomes unstable. In this case, it is difficult to control switching on or off of a p-channel metal-oxide-semiconductor (PMOS) type switch 11 and an n-channel metal-oxide-semiconductor (NMOS) type switch 12 included in the switch unit 1 at a desired level, thereby preventing a current of an inductor used in the boost type DC-to-DC converter from being controlled.
The PMOS type switch 11 and the NMOS type switch 12 of the switch unit 1 cannot be controlled because the driving voltage for driving the switch control circuit unit 2 is low. As a result, a current of the inductor in the DC-to-DC converter increases to a saturation point, and thus damaging the PMOS type switch 11.